Kingella kingae is a fastidious gram-negative coccobacillus of the Neisseriaceae family and is a normal inhabitant of the human oropharyngeal flora. This bacterium belongs to HACEK group and can cause infective endocarditis. Recently, as the result of improved isolation and identification techniques, an increasing number on invasive K. kingae infections have been reported throughout the world, suggesting that the organism is an important cause of heart and skeletal infections in pediatric and adult patients. Despite the emerging body of information on the clinical and diagnostic aspects of K.kingae infections, the virulence mechanisms of this pathogen remain largely unknown. Our results suggest that K. kingae produces a potent proteinaceious leukotoxin (Ktx) that is associated with cell membranes. This is the first evidence of a K. kingae leukotoxin that may be an important virulence factor for evasion of the host immune response during infection. The goal of this research is identify and characterize Ktx. In the proposed research we will: - Study distribution of Ktx in different K. kingae clinical isolates;- Sequence K. kingae genome;- Purify Ktx from K. kingae followed by the protein identification;- Identify ktx gene and generate ktx mutants using random and site-directed mutagenesis approaches;- Characterize Ktx toxicity to different human cells. Identification of K. kingae virulence factors will be essential to understanding how the pathogen causes disease. The results obtained in this study will have significance for the prevention and treatment of K. kingae infections. PUBLIC HEALTH RELEVANCE: Kingella kingae is a human oral bacterium that can cause infections of heart and skeletal system. We propose to characterize K. kingae toxin that can destroy human white blood cells. The results obtained in this study will have significance for the prevention and treatment of K. kingae infections.